1. Field of the Invention
The present invention relates to fiber optical measurement tools, and particularly to tools for detecting the presence of light signals in optical fibers or cables.
2. Discussion of the Known Art
So-called live optical fiber identifier tools are generally known. See, e.g., U.S. Pat. No. 5,708,499 (Jan. 13, 1998); and U.S. Patent Appl'n Pub. No. 2008/0192241 (Aug. 14, 2008). FIGS. 1 and 2 of the present application show side and front views of a live fiber identifier tool 1 available from OFS Fitel, LLC, Norcross, Ga. 30071, as model No. ID-H/R.
The known live fiber identifier tools indicate the direction in which a signal is traveling in a single optical fiber within a cable, or in a fiber selected from among a number of ribboned fibers, without disconnecting the cable or otherwise disrupting traffic in an associated network. A length of the cable or fiber is inserted through a slot or groove 2 defined in a fiber detection head portion 3 of the tool 1, as shown in FIGS. 1 and 2. The user then pulls a lever or trigger 4 downward, causing a clamp in the head portion 3 to urge the cable into a darkened recess or chamber inside the head portion, and to force the cable to bend inside the recess by a certain amount. The tool 1 also has a control panel 5 including a power on/off switch 6, signal direction indicator lamps 7, and a tool status and measurement data display screen 8.
Two photo detectors are mounted at determined locations inside the head portion 3 (see FIG. 3 and related description below). A small fraction of any light signal traveling in the cable fiber will leak from the fiber and exit from the cable bend, and the photo detectors are located so that depending on the direction of the light signal in the fiber, one of the detectors receives more of the light that exits the cable than the other detector. Live fiber identifier tools are generally quite effective and often used in fiber optic data centers, FTTx, and related applications.
Optical cables that contain a pair of fibers rather than just a single fiber are also being used more frequently at many data centers. For example, Google® and Bank of America® recently started to deploy dual bend insensitive multimode fiber (BIMF) cables at their main and sub-database centers. With such dual fiber cables, it becomes possible for two different light signals to travel through respective fibers in opposite directions along the same cable, at any given time. The existing live fiber identifier tools operate only indicate the direction a light signal is traveling along a cable containing a single fiber, however. Therefore, in order to operate and maintain modern data centers like those mentioned above, there is a need for a tool capable of indicating the presence and direction of light signals that may travel along a dual fiber cable in just one or in both directions at any given time.